<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /*（3）第三种是利用绝对定位布局的方式，将父级元素设置相对定位。左边元素设置为absolute定位，并且宽度设置为
    200px。将右边元素的margin-left的值设置为200px。*/
    .router {
      position: relative;
      height: 100px;
    }

    .left {
      position: absolute;
      width:200px;
      height:100px;
      background-color: tomato
    }

    .right {
      margin-left:200px;
      height: 100px;
      background-color: gold
    }
  </style>
</head>

<body>
  <div class="router">
    <div class="left">left200px</div> 
    <div class="right">right自适应</div>
  </div>
</body>

</html>